U.S. patent application number 09/909358 was filed with the patent office on 2003-01-23 for method and apparatus for fabricating complex grating structures.
Invention is credited to Park, Miri, Rogers, John.
Application Number | 20030017424 09/909358 |
Document ID | / |
Family ID | 25427098 |
Filed Date | 2003-01-23 |
United States Patent
Application |
20030017424 |
Kind Code |
A1 |
Park, Miri ; et al. |
January 23, 2003 |
Method and apparatus for fabricating complex grating structures
Abstract
An imprint lithography method provides a negative image of a
pattern formed in a fixed medium on a mechanically flexible imprint
master. A substrate includes a deformable material formed over the
substrate surface to be patterned. The fixed medium of the imprint
master contacts with the substrate to cause the deformable material
to deform and contour to the negative image of the pattern of the
fixed medium. The imprint master is decoupled from the substrate
after the pattern formed in the deformable material is solidified.
With the solidified pattern formed on the substrate, the substrate
is then patterned by etching or other means.
Inventors: |
Park, Miri; (New Providence,
NJ) ; Rogers, John; (New Providence, NJ) |
Correspondence
Address: |
CHRISTIE, PARKER & HALE, LLP
350 WEST COLORADO BOULEVARD
SUITE 500
PASADENA
CA
91105
US
|
Family ID: |
25427098 |
Appl. No.: |
09/909358 |
Filed: |
July 18, 2001 |
Current U.S.
Class: |
430/322 ;
101/3.1; 430/323; 430/330; 430/5 |
Current CPC
Class: |
G03F 7/0002 20130101;
B82Y 10/00 20130101; G03F 7/0005 20130101; B82Y 40/00 20130101 |
Class at
Publication: |
430/322 ; 430/5;
430/323; 430/330; 101/3.1 |
International
Class: |
G03F 007/00 |
Claims
What is claimed is:
1. A method for patterning a substrate comprising: providing a
substrate; providing a negative image of a pattern in a fixed
medium on a mechanically flexible imprint master; forming a
deformable material over a surface of the substrate; contacting the
deformable material with the negative image of the pattern thereby
urging the deformable material to deform into the pattern over the
surface of the substrate; removing the imprint master from the
substrate; and transferring the pattern into the substrate.
2. The method as in claim 1, in which the substrate is formed of a
mechanically flexible material and the step of removing includes
bending the substrate to remove the imprint master from the
substrate.
3. The method as in claim 1, wherein the step of providing the
negative image of the pattern comprises forming raised portions and
base portions within the fixed medium, the base portions
corresponding to the pattern.
4. The method as in claim 3, in which the step of providing the
negative image of the pattern includes forming the raised portions
to have rounded cross-sectional areas.
5. The method as in claim 1, in which the substrate includes a
composite structure of a layer of InP formed over a layer of
InGaAsP or InGaAs formed, in turn, over a layer of InP, and the
step of patterning the substrate includes forming a pattern within
the composite structure.
6. The method as in claim 1, further comprising forming a release
agent on the negative image of the pattern prior to the step of
contacting.
7. The method as in claim 6, wherein forming a release agent on the
negative image of the pattern comprises coating the negative image
of the pattern with a short chain thiol.
8. The method as in claim 1, wherein the pattern of the deformable
material is formed to include relatively thin residual sections of
the deformable material and relatively thick sections of the
deformable material and further comprising the step of removing the
relatively thin residual sections of the deformable material prior
to the step of transferring the pattern into the substrate.
9. The method as in claim 1, in which the step of providing the
negative image of the pattern includes forming the negative image
of the pattern by one of optical or e-beam lithography followed by
RIE etching.
10. The method as in claim 1, further comprising the step of
heating one of of before and during the step of contacting.
11. The method as in claim 10, wherein the heating comprises
heating above a glass transition temperature of the deformable
material.
12. The method as in claim 1, wherein the deformable material
comprises a liquid.
13. The method as in claim 1, wherein the deformable material
comprises one of photoresist and a viscous polymer.
14. The method as in claim 1, in which the pattern includes a
grating structure.
15. The method as in claim 1, in which the imprint master includes
first physical alignment structures and the substrate includes
corresponding second physical alignment structures and wherein the
first physical alignment structures are aligned to the
corresponding second physical alignment structures prior to the
step of contacting, and the first physical alignment structures
mate with the corresponding second physical alignment structures
during the step of contacting.
16. The method as in claim 15, in which the second physical
alignment structures are film segments formed over the substrate
and the first physical alignment structures are recessed portions
within the imprint master, the film segments being previously
formed portions of a semiconductor device formed on the
substrate.
17. The method as in claim 15, in which the second physical
alignment structures are raised relief features formed on the
substrate and the first physical alignment structures are recessed
portions which are recessed into the imprint master to an extent
greater than the negative image of the pattern formed on the
imprint master.
18. The method as in claim 1, wherein the step of transferring the
pattern into the substrate comprises etching the substrate using
the deformable material as a mask.
19. The method as in claim 1, wherein each of the fixed medium and
the imprint master comprises polydimethlysiloxane (PDMS).
20. The method as in claim 1, further comprising the step of curing
the pattern of deformable material after the step of contacting,
using one of a thermal treatment and UV radiation.
21. The method as in claim 1, further comprising the step of
bending the imprint master one of prior to and during the step of
contacting.
22. The method as in claim 1, in which the imprint master includes
a generally flat original configuration, further comprising the
step of bending the imprint master prior to the step of contacting,
and in which the step of contacting includes allowing the imprint
master to resile to its original flat configuration.
23. The method as in claim 1, in which the step of removing
includes bending the imprint master.
24. The method as in claim 1, in which the negative image of the
pattern includes at least one lateral dimension being less than 100
nm.
25. A lithographic imprint master formed of a mechanically flexible
material and including a pattern formed in a fixed medium thereon,
the pattern including device features having dimensions no greater
than 100 nm.
26. The lithographic imprint master as in claim 25, wherein the
lithographic imprint master is formed of a resilient material.
27. The lithographic imprint master as in claim 25, wherein the
lithographic imprint master is formed of polydimethylsiloxane
(PDMS).
28. The lithographic imprint master as in claim 25, in which the
lithographic imprint master is adapted for contacting a deformable
material formed on a surface and deforming said deformable material
into the pattern.
29. The lithographic imprint master as in claim 28, further
comprising raised alignment features formed on the surface and
corresponding recessed alignment features formed on the
lithographic imprint master.
Description
FIELD OF THE INVENTION
[0001] The present invention relates most generally to
semiconductor lasers. More particularly, the present invention
provides a method and apparatus for forming grating structures used
in conjunction with semiconductor lasers and other structures.
BACKGROUND OF THE INVENTION
[0002] Grating structures are used in conjunction with distributed
feedback (DFB) lasers, DBR (distributed Bragg reflector) structures
and other mirror and laser structures formed in the semiconductor
and optoelectronics industries. More particularly, grating
structures are used to form portions of the mirror and laser
structures. A grating structure includes a grating period
consisting of a repeating sequence of materials having different
refractive indices. A DFB laser, for example, may use the grating
structure, also referred to as a grating reflector to tune the
laser by adjusting the wavelength of the laser light. A standard
DFB laser may include grating periods equivalent to approximately
one-half of the wavelength of the light being propagated. By
changing or interrupting the grating period, the wavelength of the
propagated light may be changed.
[0003] It is therefore critical to accurately produce grating
structures having the desired grating period or periods. Grating
structures are commonly formed on substrates using e-beam or
holographic methods to produce an alternating series of adjacent
lines which may include lateral dimensions as small as 10
nanometers. E-beam technologies are very expensive and
time-consuming. Holographic techniques are rather difficult to
control, especially when producing arrays of grating structures
which include multiple grating periods.
[0004] The present invention is therefore directed to providing an
improved method and apparatus for reliably and accurately forming
patterns such as grating structures on semiconductor
substrates.
SUMMARY OF THE INVENTION
[0005] The present invention provides a method and apparatus for
repeatably and accurately producing a pattern in a substrate, such
as a grating pattern. The method includes first forming a negative
image of the desired pattern in a fixed medium. The fixed medium is
formed on an imprint master which may be rigid or mechanically
flexible. The imprint master is reusable. After the negative image
of the pattern is formed, the imprint master is pressed against a
substrate coated with a deformable viscous or liquid material. The
deformable material deforms and contours to the negative image
formed in the fixed medium, producing the desired pattern on the
substrate. The deformable material is then solidified to form a
fixed pattern. The pattern may be fixed by curing, for example, by
thermal treatment or UV radiation or other appropriate curing
means. The solidified fixed pattern formed in the deformable
material on the substrate surface is then transferred into the
substrate by etching or other means. The top surface of the
substrate may include a layer or layers of different materials
which may be patterned by the etching process.
[0006] It is to be understood that both the foregoing general
description and the following detailed descriptions are exemplary
but not restrictive of the invention.
BRIEF DESCRIPTION OF THE DRAWING
[0007] The invention is best understood from the following detailed
description when read in conjunction with the accompanying drawing.
It is emphasized that, according to common practice, the various
features of the drawing are not to scale. On the contrary, the
dimensions of the various features and the relative dimensions and
locations of the features are arbitrarily expanded or reduced for
clarity. Each of the figures is a cross-sectional view.
[0008] FIG. 1 shows an exemplary negative pattern formed in an
exemplary imprint master;
[0009] FIG. 2 shows a molding layer formed over grating layers
formed on the substrate;
[0010] FIG. 3 shows the exemplary imprint master of FIG. 1
positioned over the substrate of FIG. 2;
[0011] FIG. 4 shows an exemplary flexible imprint master positioned
over the substrate of FIG. 2;
[0012] FIG. 5 shows another exemplary flexible imprint master
positioned over the substrate of FIG. 2; FIG. 6 shows the imprint
master in contact with the substrate being patterned;
[0013] FIG. 7 shows the patterned substrate;
[0014] FIG. 8 shows the patterned and etched substrate;
[0015] FIG. 9 shows an exemplary embodiment of the imprint
master/substrate arrangement including additional relief features;
and
[0016] FIG. 10 shows another exemplary embodiment of the imprint
master/substrate arrangement including additional relief
features.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present invention provides a manufacturable method and
apparatus for imprinting lithography. The method may be used to
fabricate structures having feature sizes of 100 nm and less, for
example, complex grating patterns, grating arrays and devices with
locally controlled grating periods. Features having lateral
dimensions on the order of 10 nm, may be produced. The present
invention finds application in DFB laser arrays, wide band
detectors with grating array filters for wavelength selection, DBR
laser arrays, and any of various other semiconductor or
optoelectronic devices.
[0018] FIG. 1 is a cross-sectional view showing an exemplary
embodiment of imprint master 1. Imprint master 1 includes pattern 9
formed within fixed medium 3.
[0019] Pattern 9 includes raised portions 7 and depressed portions
5. Fixed medium 3 may be formed of hard materials, such as silicon
and other semiconductor materials, cross-linked polymers, plastics,
and other materials. According to an exemplary embodiment, imprint
master 1 may be formed entirely of the materials which form fixed
medium 3, and in another exemplary embodiment as illustrated in
FIG. 1, imprint master 1 may be a composite member including fixed
medium 3 as a top portion and also including bulk portion 2 formed
of another material. Bulk portion 2 of imprint master 1 may be
formed of a material such as silicon, cross-linked polymers,
plastics and other materials, and may be generally rigid according
to an exemplary embodiment. According to another exemplary
embodiment, bulk portion 2 of imprint master 1 may be formed of a
mechanically flexible material, such as PDMS
(Polydimethylsiloxane). According to yet another exemplary
embodiment, imprint master 1 may include fixed medium 3 formed of a
mechanically flexible material such as PDMS and bulk portion 2 may
be formed of a harder material, such as silicon or glass which is
formed thin enough to be somewhat bendable. According to yet
another exemplary embodiment, each of bulk portion 2 and fixed
medium 3 may be formed of PDMS.
[0020] Pattern 9 may be formed by e-beam, optical or other
lithography methods, followed by an etching process, such as RIE
(Reactive Ion Etching). Pattern 9 may also be formed by plastic or
polymer molding techniques. Each of the foregoing embodiments are
exemplary and other patterning methods may alternatively be used.
Pattern 9 includes raised portions 7 and recessed portions 5.
According to the exemplary embodiment in which imprint master 1 is
a composite member. Including bulk portion 2 and fixed medium 3,
pattern 9 may be formed entirely within fixed medium 3 as shown in
FIG. 1, or surface 6 may represent the top of bulk portion 2 such
that only raised portions 7 are formed of fixed medium 3. Pattern
9, so formed, is designated a negative image of the desired
pattern, and it will be shown in subsequent figures that the
pattern formed in the substrate is the negative or opposite of
pattern 9 formed in fixed medium 3 of imprint master 1. Stated
alternatively, raised portions 7 of pattern 9 of imprint master 1
will produce etched or recessed sections in the patterned
substrate. Conversely, recessed portions 5 of pattern 9 of imprint
master will form unetched or raised portions of the substrate after
patterning such as by etching. Pattern 9 may be a grating pattern
or any of various other patterns and may include critical
dimensions (feature sizes and spacings between features) less than
100 nm and as low as 10 nm. Raised portions 7 may have
substantially orthogonal edges such as edge 10 or they may include
rounded edges such as rounded edges 12. Rounded edges 12 offer the
advantage of reduced stress created in the pattern later formed on
a deformable material. Such stress can result in cracking. For
simplicity, raised features 7 will be shown with orthogonal edges
in subsequent figures.
[0021] Additionally, in subsequent figures, imprint master 1 will
be shown to be formed entirely of the same material as fixed medium
3, and therefore bulk portion 2 will not be shown.
[0022] FIG. 2 shows substrate 15 with various layers formed upon
it. Substrate 15 may be a silicon, gallium arsenide (GaAs) or
indium phosphide (InP) substrate or other suitable substrate
materials used in the semiconductor and optoelectronics
manufacturing industries. According to other exemplary embodiments,
substrate 15 may be a mechanically flexible member. According to
the exemplary embodiment shown in FIG. 2, three layers are formed
over substrate 15. According to an exemplary embodiment, each of
layers 17, 19, and 21, which form the composite structure over
substrate 15, may be a film formed by epitaxial methods, such as
MBE (Molecular Beam Epitaxy). Other formation methods, such as
various plasma deposition techniques, may be used in other
exemplary embodiments. According to the exemplary embodiment shown
in FIG. 2, lower layer 17 may represent an InP layer; central layer
19 may represent either an InGaAsP layer or a ternary InGaAs layer;
upper layer 21 may represent another InP layer; and, substrate 15
may be formed of InP. This is intended to be exemplary only, and
the composite film structure may include more or fewer layers than
the three shown in FIG. 2. Furthermore, the layers which together
form the composite structure, may be formed of various other
suitable materials, and according to various other formation
methods. In a preferred embodiment, the composite structure may be
subsequently patterned according to the present invention to form a
grating pattern. Various other patterns may be formed
alternatively. According to another exemplary embodiment, substrate
15 may not include any layers formed thereon and the substrate
itself may be etched and therefore patterned.
[0023] Molding layer 25 is formed over the top surface of the
substrate which is top surface 23 of film 21 in the exemplary
embodiment. Molding layer 25 is a deformable, viscous material
which deforms or flows when contacted by imprint master 1.
According to an exemplary embodiment, molding layer 25 may be a
liquid. According to an alternative embodiment, molding layer 25
may not deform until heated above a critical temperature such as
its glass transition temperature-T.sub.g. Molding layer 25 is
formed over top surface 23 of substrate 15 according to
conventional methods, such as by spin-coating or other coating
methods. Other methods for forming molding layer 25 over substrate
15 may also be used. According to an exemplary embodiment, molding
layer 25 may be a photoresist material, such as commercially
available G-line or i-line photoresists. Other readily deformable,
viscous polymer or liquid layers may be used alternatively. Molding
film 25 is chosen for compatibility with the substrate and imprint
master materials as well as the subsequent processes to be
performed on the substrate. According to the embodiment in which
heat is applied to urge the deformation of the molding layer,
molding layer 25 is chosen to be deformable at a glass transition
or other reflow temperature compatible with the materials of which
imprint master 1 and fixed medium 3 are formed. The materials are
chosen to assure that when molding layer 25 is deformed by heating
to its glass transition temperature while being pressed against
pattern 9 formed in fixed medium 3 of imprint master 1, for
example, pattern 9 does not become distorted. Molding layer 25 is
chosen to be easily released from imprint master 1 after
patterning. Molding layer 25 is also chosen in conjunction with the
etching process which will subsequently be used to etch the
substrate or the films formed on the substrate so as to produce a
selective etch process and one in which molding layer 25 is not
substantially attacked during the etching process used to etch the
layers or substrate 15. Furthermore, molding layer 25 is chosen to
be chemically unreactive towards fixed medium 3 and imprint master
1, and easily removed after the etching process.
[0024] Now turning to FIG. 3, imprint master 1 is inverted so that
pattern 9 faces top surface 27 of molding layer 25. Imprint master
1 includes upper or leading surface 11, which represents the upper
surface of raised features 7 of imprint master 1. Before force is
applied along opposed directions 28 and 29, the facing surface of
the imprint master and/or top surface 27 of molding layer 25, may
be chemically treated or coated with a release agent. The chemical
treatment or release agent is chosen in conjunction with molding
layer 25 to ensure that after imprint master 1 is pressed against
substrate to form a pattern in molding layer 25, imprint master 1
can be easily removed from molding layer 25 without distorting the
pattern formed in molding layer 25. According to an exemplary
embodiment, a short-chain thiol, such as alkyl thiol, may be used
as a release agent. According to other exemplary embodiments,
various hydrophobic layers such as fluorinated silane, and other
suitable release agents, may be used alternatively.
[0025] To form a pattern within molding layer 25, pattern 9 formed
in imprint master 1 is contacted with molding layer 25 after the
opposed leading surfaces are positioned substantially parallel to
one another and imprint master 1 and substrate 15 are aligned to
each other. At least a component of force is supplied along either
or both of opposed directions 28 and 29. A machine press or other
suitable apparatus may be used to uniformly press the components
against each other. The uniformity of the force applied along
opposed directions 28 and 29 at various lateral locations of the
components and which is used to uniformly force the components
together, may be carefully controlled by various suitable means.
Molding layer 25 is chosen such that, even at room temperature,
extensive force is not required. The precise magnitude of force
will vary according to choice of fixed medium 3 of imprint master
1. In the case in which molding layer 25 is a liquid, only minimal
force will be required to simply bring imprint master 1 into
contact with molding material 25, in order to create a pattern in
molding layer 25.
[0026] According to the exemplary embodiment in which fixed medium
3 and imprint master 1 are formed of a bendable or mechanically
flexible material, such as PDMS, a roller or other mechanical
device may be passed over the top surface to ensure uniform contact
between leading surfaces 11 of imprint master 1 and substrate 15.
Mechanically flexible imprint master 1 will be generally flat and
may be bent in order to contact a first portion of molding layer
25, then allowed or urged back into its original flat position to
uniformly contact the entirety of molding layer 25. Such a
technique prevents air bubbles from being trapped between imprint
master and substrate 15. Such air bubbles can distort the pattern
being formed.
[0027] According to one exemplary embodiment, originally-flat
imprint master 1 may be bent or bowed slightly so that central
portion 41 of imprint master 1 first contacts molding layer 25
formed over substrate 15. This is shown in FIG. 4. Peripheral
portions of imprint master 1 are then allowed or urged to contact
molding layer 25 of substrate 15 to ensure that bubbles or other
anomalies do not form between imprint master 1 and molding layer 25
and thereby distort the pattern. Imprint master 1 is thereby
restored to its original flat configuration. According to an
exemplary embodiment, imprint master 1 will be formed of a
mechanically flexible, yet resilient material which resists bending
and returns to its originally flat configuration due to its own
resiliency. Conventional mechanical methods may be used to slightly
bow imprint master 1, then uniformly press imprint master 1 over
substrate 15. According to this exemplary embodiment, each of
imprint master 1 and fixed medium 3 may be formed of PDMS.
[0028] According to another exemplary embodiment in which imprint
master 1 is formed of a mechanically flexible material as shown in
FIG. 5, originally-flat imprint master may be bent slightly and
brought into contact with substrate 15 such that an edge portion
such as edge portion 14 of imprint master 1 first contacts top
surface 27 of molding layer 25. Imprint master 1 is then bent or
allowed or urged to be restored to its original flat shape in order
to uniformly contact the entirety of molding layer 25. A roller may
be used, for example. According to either of the embodiments shown
in FIGS. 3,4 and 5, after imprint master 1 is initially brought
into contact with molding layer 25 of substrate 15, it will be
essentially flat over substrate 15 as will be shown in FIG. 6.
[0029] According to an alternative embodiment, substrate 15 may be
heated to promote viscosity of deformable molding layer 25. Heat
may be applied to the substrate prior to pressing the components
against each other, heat may be applied during the process of
pressing the components against one another, or heat may be applied
at both of the aforementioned stages of the process. Heat may be
applied by various suitable and conventional means. For example,
substrate 25 may be seated on a hotplate or the machine press or
other apparatus which may house the units being contacted against
each other, may include a heated chamber, such as a chamber heated
by convection. The heat applied is sufficient to raise the
temperature of molding layer 25 above a critical value such as its
glass transition temperature, T.sub.g. This ensures that molding
layer 25 is in a deformable or viscous state when it is brought
into contact with pattern of imprint master 1.
[0030] FIG. 6 shows the two components pressed against each other.
Leading surface 11 of imprint master 1 preferably contacts top
surface 23 of upper film 21 formed on substrate 15. Molding layer
25, which is in a deformable or viscous state, conforms to the
features of pattern 9 formed in imprint master 1. If a "pattern" is
considered to be raised features off of a surface, it can be seen
that the desired pattern formed within molding layer 25 over
substrate 15 is the negative image of pattern 9 formed in imprint
master 1. Width 26 of features formed in molding layer 25 and
spacing 38 formed between the features of molding layer 25 may be
on the order of 100 nm or less. These features and spaces will be
translated into features and spaces on the substrate. According to
an exemplary embodiment, dimensions such as width and spacing 38
may be as low as 10 nm.
[0031] The pattern formed in molding layer 25 is then fixed.
Various solidification techniques may be used to fix molding layer
25, depending on the material of which molding layer 25 is formed.
Curing, for example, by thermal treatment or UV-radiation may be
used in various exemplary embodiments in which molding layer 25 is
a polymeric material. Other appropriate curing means may be used
alternatively. According to the exemplary embodiment in which
heating was used to promote the viscosity of molding layer 25, a
cooling process may be used to solidify molding layer 25.
[0032] After molding layer 25 is solidified, imprint master 1 is
removed from the arrangement. Conventional cooling methods may be
used if heat was applied during the molding or curing process.
According to the exemplary embodiments in which either or both of
the imprint master and the substrate are formed of a mechanically
flexible material, the coupled components (imprint master 1 and
substrate 15) may be decoupled by peeling or slightly bending the
mechanically flexible component or components, thereby separating
them from one another. Various other conventional mechanical means
may be used to decouple the components without distorting the
features of the pattern formed on the substrate. Imprint master 1
may then be cleaned using conventional methods, then reused.
[0033] FIG. 7 shows substrate 15 after imprint master 1 has been
decoupled from the arrangement. Desired pattern 30 formed of
molding layer 25 over surface 23 of substrate 15, includes spaces
or void areas 37 and features 35. Features 35 correspond to
recessed portions 5 of pattern 9 formed in imprint master 1.
Conversely, spaces or void areas 37 correspond to features 7 formed
in the negative image of the pattern, i.e. pattern 9 of imprint
master 1. It should again be emphasized that desired pattern 30 is
exemplary only and that any of various patterns including single or
multiple grating structures or other features may be formed. At
this point, pattern 9 may optionally be solidified by thermal,
UV-radiation or other suitable curing means.
[0034] Void areas 37 of desired pattern 30, may include a small
amount of molding layer 25 residual on surface 23. In a preferred
embodiment, surface 23 will be void of molding layer 25 in void
areas 37. As such, a relatively thin section of molding layer 25 is
shown as thin residue layer 39 in some of void areas 37 shown in
FIG. 7. Features 35 therefore represent a relatively thick portion
of molding layer 25 and void areas 37 may include a thin residue
layer 39 of molding layer 25 over substrate 15. Thin residue layer
39 may alternatively be referred to as a scumming layer. The
illustration of FIG. 7 is intended to be exemplary only and all of
void areas 37 may be free of molding layer 25 according to other
exemplary embodiments; conversely, each of void areas 37 may
include thin residue layer 39 of molding layer 25, according to
other exemplary embodiments. After desired pattern 30 is formed,
the substrate is ready to be etched.
[0035] According to an exemplary embodiment, prior to the etching
of the substrate, desired pattern 30 consists of relatively thick
portions 35 of molding layer 25 and relatively thin residue
portions 39 of molding layer 25. The relatively thin residue
portions 39 of molding layer 25 formed within void regions 37, may
be removed using reactive ion etching, or other conventional and
suitable "de-Scum" methods. According to an exemplary embodiment,
this removal step may be performed in-situ with the etching process
subsequently used to etch substrate 15.
[0036] Now turning to FIG. 8, substrate 15 is shown after the
substrate has been etched using desired pattern 30 formed in
molding layer 25, as a masking medium. FIG. 8 shows that the
sections of layers 17,19 and 21 which were not protected by thick
portions 35 of molding material 25, have been removed by etching.
The etching process is carried out after any residual thickness of
the molding film has been removed from void areas 37. Various
suitable etching processes may be used. The etching process is
chosen in conjunction with the films to be etched. According to an
exemplary embodiment, RIE etching may be used. A selective etching
process is chosen so that relatively thick portions 35 of molding
film 25 will be substantially intact during and after the etching
process. Desired pattern 30, which has been translated from the
molding film into the substrate, may be any of various patterns. It
may include a single grating period as grating period 31. It may
include a single grating period having a larger pitch such as
grating period 33. Pattern 30 may also include multiple grating
periods such as each of grating period 31 and grating period 33
shown in FIG. 8. It should be emphasized at this point that the
structure shown in FIG. 8 is exemplary only and that any of various
other patterns may be formed in the substrate according to this
procedure. This procedure is not intended to be limited to forming
grating patterns.
[0037] After the structure illustrated in FIG. 8 is achieved by
etching, conventional methods may be used to remove molding film 25
from over the substrate. Various subsequent processing operations
may then be carried out upon the substrate which has been etched to
include desired pattern 30. For example, in the exemplary
embodiment in which grating period or periods are formed, and in
which lower film 17 and upper film 21 are each formed of InP, and
according to the case in which central layer 19 is formed of one of
InGaAs or InGaAsP, void areas 37 between the etched features may be
subsequently filled in with InP according to the embodiment in
which a grating period is formed either below or above an active
layer along which light will be propagated. The above recited films
and structures are intended to be exemplary only.
[0038] According to another aspect of this invention and as in the
exemplary embodiment shown in FIG. 9, each of substrate 115 and
imprint master 101 may be formed to include corresponding alignment
structures. In an exemplary embodiment, the alignment structures
may include raised portions, such as raised portions 144 formed
over surface 123 of substrate 115. Corresponding recessed portions
142 are formed in imprint master 101, such that raised portions 144
mate with corresponding recessed portions 142 and top surfaces 146
of raised portions 144 and recessed surfaces 140 of recessed
portions 142 of imprint master 101, are in contact with each other
when the components are in contact with each other. Recessed
portions 142 are recessed to an extent greater than the base
portions 105 of the portion formed in imprint master 101. According
to another embodiment, the disposition of the corresponding raised
and recessed portions may be reversed such that recessed portions
142 are formed on substrate 115. The components are pressed against
each other after a molding film (not shown) is formed over
substrate surface 123 as described in conjunction with FIGS. 1-8
and after the corresponding alignment features are aligned to one
another. According to an exemplary embodiment, the corresponding
alignment structures 142 and 144 may be disposed peripherally on
the substrate.
[0039] The corresponding alignment structures are aligned to one
another before imprint master 101 and substrate 115 are brought
into contact with one another. The corresponding alignment
structures are formed and positioned to ensure that, when engaged,
the patterns are aligned with respect to lateral 150 and rotational
directions, and thickness 148 and depth 149 are chosen to ensure
that imprint master 101 is disposed in the desired vertical
location with respect to substrate 115 when the components are
joined. This is especially critical when a pattern has already been
formed within substrate 115. Such a pattern is shown to include
raised portions 151 and recessed portions 152. Height 148 of raised
portions 144 may be chosen such that, when a molding layer (not
shown) is formed over substrate 123 such as by coating, for
example, it will not extend above top surfaces 146. According to
the embodiment in which the substrate has previously had
topographical features formed upon it by various patterning
methods, the height of raised features 107 of imprint master 101 is
chosen to ensure that, after the deformable molding material (not
shown) is molded into a pattern, the height of the molding material
formed after patterning is sufficient to enable an etching or
similar process to be carried out on various regions of the
already-patterned substrate in order to further pattern the
substrate.
[0040] According to yet another aspect of this invention, such as
illustrated in FIG. 10, imprint master 201 may include relief
features formed to mate with corresponding physical device features
formed on substrate 215. For example, if raised features such as
exemplary discrete device features 244 are formed on portions of
substrate 215 not being presently patterned using imprint master
201, imprint master 201 may include recessed regions 242
corresponding to the locations on substrate 215 where device
feature 244 is disposed. Device feature 244 may be a segment of an
oxide layer, according to an exemplary embodiment. Molding layer
225 may be formed over surface 223 by a procedure and to a
thickness such that it covers the raised features such as device
feature 244 as shown in FIG. 10. Alternatively, molding layer 225
may be formed so as not to extend over device feature 244.
According to either exemplary embodiment, the patterning process is
then carried out as described in conjunction with FIGS. 1-8. It can
be seen that recessed regions 242 are recessed into imprint master
201 to a greater extent than pattern 209 formed on imprint master
201. According to another exemplary embodiment, the extent of
recession of recessed regions 242 may be less than or equal to the
depth of pattern 209 formed on imprint master 201.
[0041] The preceding merely illustrates the principles of the
invention. It will thus be appreciated that those skilled in the
art will be able to devise various arrangements which, although not
explicitly described or shown herein, embody the principles of the
invention and are included within its spirit and scope.
Furthermore, all examples and conditional language recited herein
are principally intended expressly to be only for pedagogical
purposes and to aid the reader in understanding the principles of
the invention and the concepts contributed by the inventors to
furthering the art, and are to be construed as being without
limitation to such specifically recited examples and conditions.
For example, the substrate itself may be etched into a pattern
according to the method disclosed, and various other films and
combinations thereof may be formed over the substrate and then
etched according to the process disclosed above. Furthermore, the
pattern formed according to this method may represent a grating
period, several grating periods, an array of grating periods or any
other pattern required to be formed over a substrate in the
semiconductor or optoelectronics manufacturing industry. The
pattern may include features transverse to the cross-sectional view
of the pattern which are shown in the figures.
[0042] Moreover, all statements herein reciting principles,
aspects, and embodiments of the invention, as well as specific
examples thereof, are intended to encompass both structural and
functional equivalents thereof. Additionally, it is intended that
such equivalents include both currently known equivalents, such as
equivalents developed in the future, i.e., any elements developed
that perform the same function, regardless of structure. The scope
of the present invention, therefore, is not intended to be limited
to the exemplary embodiments shown and described herein. Rather,
the scope and spirit of the present invention is embodied by the
appended claims.
* * * * *